1. Field of the Invention
The present invention relates generally to apparatus for testing surface hardness of a specimen, and, more paticularly, to a novel and improved hardness testing apparatus adapted to accurately sense variations in surface hardness among a succession of adjacent test surface portions.
2. Prior Art
Hardness testing apparatus of the "continuous" type adapted to measure variations in surface hardness among a succession of adjacent test surface portions is known. One known device of this type utilizes a pair of members which are pivoted side-by-side and close to each other on a slide, and which can move in an end plate. The members both engage a test surface and are configured such that relative movement can be effected between the test surface and the members in directions paralleling the plane of the test surface so that the members are brought into engagement with a succession of adjacent test surface portions. One of the members is known as a "penetration member" and is loaded in a controlled manner, causing it to penetrate the test surface. The other of the members is a "sensor member" and it is simply held in firm, non-penetrative engagement with the test surface. A relative motion sensing transducer is interposed between the two members to sense their relative movement, whereby the transducer's output signal is representative of the depth to which the penetration member has penetrated the test surface at a given time.
As is understood by those skilled in the art, the depth to which the penetration member has penetrated the test surface, in response to a particular loading of the penetration member, is a function of surface hardness. Surface hardness can be ascertained from knowledge of the penetration depth, knowledge of the loading of the penetration member, and knowledge of construction of such portions of the penetration member as are caused to penetrate the test surface.
The proposed device utilizes a first transducer to sense relative movement between the penetration and sensor members, and a second transducer to sense relative movement between the slide and the base of the device. By this arrangement, an orthogonal or "X-Y" plot can be made with sensed hardness represented by units of distance along one axis and with position along the test surface represented by units of distance along an orthogonally extending axis.
A problem with the proposed device is that the sliding motion which takes place with its construction and arrangement of components results in the relatively large force required to move the penetration member being applied along the test surface, and deformations caused by this force are found to act, at least partially, on the sensor member. When these forces act on the sensor member, distortions may be introduced into the test results, particularly with regard to the measurement of travel sensed by the transducer attached to the slide.